Cathode ray tube



Nov. 17, 1959 1.. SWEDLUND 2,913,512

CATHODE RAY TUBE Filed Oct. 29, 1956 FIGZ. F|G.|.

q FIG.3. I 0 10g INVENTORI LLOYD E. SWEDLUND,

United States Patent 051cc Patented Nov. 17, 1959 CATHODE RAY TUBE Lloyd E. swenunm Witt, N.Y., assignor to General Electric Company, a corporation of New York Application October 29, 1956, Serial No. 618,743

6 Claims. (Cl. 313-76) This invention relates to improvements in electron guns for cathode ray tubes and the like wherein elimination of negative ions fromthe electron beam is desired.

Cathode rayv tube electron guns. are known in' which negative ion trapping is accomplished by-bending the electron beam and its associatedion stream to a' direction such that theelectrons and ions will not pass 'a limiting which it is impractical to obtain, the path of the electron beam, after passing through the ion trapping system is at an angle to the principal axis of the electron gun;

In order to line up .the emerging electron beam of such a gun with the axis of the tube, it has been proposed in the prior art to tilt the gun as a whole with respect to the tube axis. However this has the disadvantage that the neck diameter of the tube must be enlarged to accom-. modate the parts moved oit the neck axis by tilting the electron gun. In an alternative arrangement of the prior coaxial relation with the tube neck, yet eliminates the need for bending of the gun or tilting, of any of the .gun parts with respect to the tube neck axis.

These and other objects of the. present invention .will be apparent from the following description taken in conjunction with the accompanying drawing, and the scope of the invention will be defined in the appended claims. Briefly, in accordance with a preferred aspect of the present invention lrprovide a cathode ray tube electron gun of which all of the electrodes except the cathode and control grid are adapted to be supported coaxially within the neck of the tube, and in which the electron beamds originated with the initial portion of its path parallel to but transversely displaced from the axis of the tube neck. The beam is then subjected to the combined influence of an electrostatic field acting to deflect it toward the axis of the neck and the magnetic field of a single external ion trap magnet acting to deflect it in the opposite'direction, with the. net effect on the electrons and associated negative ions beingsuch as to direct the ions across the axis of the gun and against a trapping surface while the electrons are redeflected so as to emerge from the limiting aperture of the gun on apath substantially coincident with the axis of the tube neck. r

Figure 1 is a partly sectionalized view of a portion of a cathode ray tube having an electron gun constructed in accordance with the present invention.

Figure 2 is a view similar to Fig. 1 illustrating another embodiment of an electron gun constructed in accordance with the present invention.

Figure 3 illustrates a modified form of a portion of the structure shown in Figure .2.

, -Turning to Figure 1, one embodiment of an electron gun constructed in accordance with the present invention is shown mounted" in the neck 2 of a cathode ray tube envelope, the remainder of the envelope not being shown.

art, a portion of the gun is bent or tilted with respect to the remainder, the tilt being such that the initial direction of the electron beam is at an angle to the neck of the tube. This eliminates the need for bending the electron beam and ion stream by an electrostatic field, and 'the effect of the corrective magnetic field is such as to bend the electron beam into coincidence with the axis of the tube at the same timejthat it is lined up for passage through the limiting, aperture at the exit end of the gun.

require parts of non-symmetrical shape, and such parts are difiicult to support and align properly within the tube neck.

Accordingly, a principal object of the present invention is to provide an improved electron gun for cathode ray tubes, and the like which requires only a single ion trap magnet and yet produces an electron-beam which emerges coaxial with the tube neck, and which is so constructed and arranged as to be accommodated. in a tube neck of minimum diameter.

Another object is to provide a cathode ray tube electron gun for producing a coaxial, substantially ion-free 'electron beam in a .tube neck ofmini-mum diameter, and ,whose parts may be easily fabricated, aligned, and supported in the tube neck.

Another. object is to provide an electron gun' for a cathode ray. tube or the like which is adapted to be mounted within and in coaxial relation with the tube neck,

and which produces an electron beam which emerges in The gun includes an accelerating anode 4 of generally tubular shape and having a diminished diameter portion 6 at one end terminating in a transversepartitionS formed with a central electron beam limiting'aperture 10. Anode 4 has an axis 11 which is coincident with the axis of neck 2 and defines the major axis of. the electrongun. Another accelerating electrode 12 is arrange'd'in spaced coaxial relation'with accelerating electrode 4, and a coaxial cylindrical focus electrode 26 overlaps the adjacent ends of the accelerating electrodes 4, 12. Electrodes 4, Hand .20 are maintained in alignment and supported in coaxial relation with neck 2 by straps 14 extending into supporting insulating rods, a portion of one which is shown at M, and by spring clips "18 which engage the interior wall of the neck. The accelerating anodes 4, 12 are connected to a source of suitable operating potential through the spring clips 18 and a conductive coating 22 contacted thereby on the interior wall of the neck. The focus electrode 20 is connected to a source of desired potential by a lead 57 sealed through the baseend of the neck 2.

Coaxially mounted opposite thelarger or'. base end of accelerating anode 4 and supported by rods 16 is a cupshaped screen grid 30 having a cylindricalside wall 32 of the same diameter as anode 4, and having a transverse bottom wall 34 normal to the gun axis 11. The adjacent ends of the screen grid 30 and accelerating anode 4 are formed parallel to each other but at an ,angle to the neck axis so as to provide an asymmetric electrostatic field betweentheseelectrodes, as indicated by the configuration of equipotential lines 36. The screen grid 3% is maintained in alignment with anode 4 by rods 16, the equal diameter and coaxial arrangement of the screen grid facilitating alignment oi the parts and-insuring a mechanically strong assembly. Adjacent the screengrid is a cup-"shaped control grid 40 having a cylindrical side wall 42 and a transverse end wall 44 formed with a central aperture 46. The control grid is mounted with the axis of its side wall 42 parallel to but transversely displaced from the axis of electrodes 4 and 30 in a direction opposite to the direction of tilt of the electrostatic field between electrodes 4 and 30. Coaxially supported within the control grid is a cathode 48 having an electron emitting surface 50 spaced opposite from and concentric with the control grid aperture 44.- Within the cathode is a heater 52 energized through leads 54. The control grid and screen grid are supplied the desired operating potentials through leads 56.

With the parts thus arranged, the electron beam emerging from the aperture 46 in the control grid has an initial path parallel to but transversely displaced from the major axis 11 of the gun. The transverse wall 34 of the screen grid 30 is provided with an eccentric aperture 60 positioned opposite control grid aperture 46 so that the centers of apertures 46 and 60 define a line parallel to the gun axis. The mixed beam of electrons and ions emerging from aperture 46 thus passes through aperture 60 to the tilted electrostatic field between screen grid 30 and accelerating anode 4, and by the influence of the electrostatic field both the electrons and ions of the beam are urged toward the gun axis 11, i.e. to the right as viewed in Fig. 1.

A singe magnet 64 is provided outside the neck of the tube, creating a magnetic field transverse to the axis of the gun such as to deflect the electron beam to the left as shown in Fig. 1. As is well known the magnetic field influences the trajectory of the electrons without appreciably affecting the associated ions, and hence the combined elfect of the electrostatic and magnetic fields is such as to deflect the ions across the axis 1 1 and along a trajectory as illustrated by the line 66, so that the ions fail to pass through the limiting aperture 10. By virtue of the arrangement of apertures 46 and 60 so that the initial portion of its path is parallel to and transversely displaced from the gun axis, however, the electron beam is redeflected along a path as illustrated by the line 68 in Fig. 1, and emerges through the limiting aperture in coincidence with the gun and neck axis. Thus, in accordance with the present invention, even though only a single ion trap magnet is employed and the electron gun is arranged with its axis 11 coaxial with the tube neck, the electron beam emerges from the gun in coincident relation with the axis of the gun and neck and the need for tilting of any of the parts of the gun with respect to the neck axis is completely eliminated.

Figure 2 shows another embodiment of my invention. In the electron gun of Figure 2 a tubular accelerating anode 70 has an axis 72 which defines the major axis of the gun and is coincident with the axis of the tube neck 74. A transverse partition at the screen- Ward end of electrode 70 is formed with a central limiting aperture 78. Coaxial with anode 70 is a cup-shaped screen grid 80 having a cylindrical side wall equal in diameter to anode 70 and having a transverse bottom wall formed with an eccentric aperture 82. The adjacent ends of the screen grid 80 and accelerating anode 70 are parallel and normal to the gun axis 72 rather than being inclined to the neck axis as in Fig. 1. A cup-shaped control grid 84 having the same diameter as the screen grid is mounted coaxial therewith and has an eccentric aperture 86 opposite aperture 82, the centers of apertures 86 and 82 defining a line parallel to but transversely displaced from the gun axis 72. The equal diameter and coaxial arrangement of parts 70,, 80, and 84 facilitates easy alignment of the parts during assembly, and insures firm mechanical support thereof by insulating rods 42.

The cathode 88 is mounted off the gun axis of the neck with its emitting surface opposite the aperture 86 in the control grid. Support for the cathode is provided by a strap 90 mounted in an extension of one of the insulating rods 92. A single magnet 94 is disposed outside the tube neck so as to provide a magnetic field transverse to the axis of the neck in the region of the gap between the screen grid and accelerating anode 70.

The anode 70 is maintained at a suitable operating potential above that of the screen grid so as to create an electrostatic field therebetween, the field having the general configuration indicated by the equipotential lines 96 and 98. In the operation of the gun, the electron and ion beam emerging from aperture 82 and entering the electrostatic field has a direction parallelto gun axis 72 and transversely displaced therefrom. Although the field lines 98 within the screen grid are symmetrical relative thereto, the electron beam and associated ions enter the field at one side thereof, as clearly indicated in Fig. 2, and are consequently bent toward the gun axis 72. The ions thus follow the path indicated by line 97 and are trapped within anode 70. By virtue of the eccentric disposition of apertures 82, 86 on a line parallel to but transversely displaced from the gun axis, however, so that the initial portion of its path is parallel to and transversely displaced from the gun axis, the electron beam is atfected by the combined electrostatic and magnetic field in such a manner that it is first bent to the right and then redeflected to the left along a path as illustrated by the line 99 in Fig. 2, and thus passes through the limiting aperture 78 and emerges therefrom coincident with the axis 72 of the gun and the tube neck.

As a modification of the structure shown in Fig. 2, and to accentuate the effect of the electrostatic field in diverting the beam toward the axis of the neck, the ad-' jacent ends of the screen grid 80 and anode 70 may be inclined to the neck axis in the manner shown in Fig. 1 if desired. The invention also applies to triode-type electron guns, in which case the necessary electrostatic defleeting field may be formed directly between the control grid and accelerating anode of the gun, for example by providing a skirt extending axially from the apertured surface of the control grid toward the accelerating anode. Such an arrangement is illustrated in Fig. 3, wherein 100 designates the center line or axis of the tube neck, 102 designates a portion of the first accelerating anode, and 104 isa cup-shaped control grid coaxial with and equal in diameter to anode 102 and having an eccentric aperture 105. A cathode 106 is disposed within grid 104, and an upstanding skirt 108 is provided on the control grid coaxial therewith. The adjacent edges of skirt 108 and anode 102 are parallel but tilted with respect to axis 100 in the same manner as in Fig. 1, so as to create the necessary tilted electrostatic field for deflecting the electron beam toward the neck axis 100.

Thus there has been shown and described an improved electron gun which is adapted to be mounted coaxially Within the neck of a cathode ray tube or the like, and which employs but a single ion trapping magnet yet produces an electron beam having a path coincident with the tube neck axis as it leaves the gun. The invention eliminates the need for tilting any of the gun parts, or for using parts of non-symmetrical shape which are difiicult to align and assemble, and hence materially simplifies the manufacture, assembly and mounting of the gun within the tube, while reducing to a minimum the diameter of the tube neck required to accommodate the gun.

It will be appreciated by those skilled in the art that the invention may be carried out in various ways and may take various forms and embodiments other than those illustrative embodiments heretofore described. It

is to be understood that the scope of the invention is not limited by the details of the foregoing description, but will be defined in the following claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An electron gun for cathode ray tubes and the like comprising .a first tubular electrode having an axis de- 1 fining QmaJ'O a is of il q ectron gun and having a partition at oneend transverse tdsaid axis formed with a coaxial aperture, saidfirs'tie'lectrode' having an opening at its other end concentric with said axis, a second cupshapedelectrode coaxial with the first electrode and including a transverse wall having an apertureolfset from said majoraxis in one direction, and means including a cathode and 'a control grid for producing a mixed beam of electrons and ions having a path parallel to said axis but transversely spaced therefrom in'said one direction so as to pass through said second electrode aperture'and said transversely spaced part ofsaid electrostatic field, whereby upon subjection to the field of a single magnet in the vicinity of said electron lens the electrons of said mixed beam may be deflected into a path extending through the coaxial aperture of said first electrode coincident with said major axis.

2. An electron gun for cathode ray tubes and the like comprising a cylindrical accelerating electrode having an axis defining the major axis of the electron gun and adapted to be supported coaxially within the neck of a cathode ray tube, said accelerating electrode having at one end a transverse wall provided with a coaxial electron xit aperture and forming at its other and opening concentric with said axis, a cup-shaped second electrode having a cylindrical side Wall coaxial with and of substantially the same diameter as said accelerating electrode and having a transverse bottom -wall,'said acceler- 6 said accelerating electrode-exit aperture in' a path-coincidentwith said major axis. i

4; An electron -gui1'*for cathode ray tubes and the like comprising a tubular accelerating electrode adapted to 'be supported coaxially within the neck of a cathode ray tube and having at one end atransverse wall provided with a concentric electron beam-exit aperture and defining at its other end a coaxial opening, the axis of said accelcrating electrode defining 'the major' axis ofsa id electron gun, a cup-shaped-control grid havinga cylindrical side Wallcoaxial with sa-id accelerating electrode and having ating electrode and second electrode being adapted to be maintained at different potentials so as to form an electrostatic electron lens therebet-ween for deflecting toward said accelerating electrode axis electrons and ions passing through a part of said lens transversely spaced from said axis, said second electrode bottom wall having an eccentric aperture located opposite said part of said electron lens transversely spaced from said axis, and means for producing a beam of mixed electrons and ions the initial portion of the path of which extends through said eccentric aperture of said second electrode parallel to the accelerating electrode axis, whereby upon subjection to the field of a single magnet external to the tube neck the electrons of the mixed beam may be directed through said exit aperture in a'path coincident with the axis of said accelerating electrode.

3. Anelectron gun for cathode ray tubes and the like comprising a tubular accelerating electrode adapted to be supported coaxially within the neck of a cathode ray tube and having at one end a transverse wall provided with a concentric electron beam exit aperture and defining at its other end a coaxial opening, the axis of said accelerating electrode defining the major axis of said electron gun, a cathode having an electron emitting surface oilset from said major axis, a control grid having a transverse wall opposite said emitting surface provided with an aperture transversely oflfset from said major axis, a cup-shaped screen grid having a cylindrical side wall coaxial with and of substantially the same diameter as said accelerating electrode and having a trnsverse bottom wall opposite the transverse wall of said control grid provided with an eccentric aperture aligned concentrically major axis said accelerating electrode and screen grid being'adapted to be maintained at different potentials a transverse bottom wall provided with an aperture transversely offset from:said major axis, a cup-shaped screen grid betweenuthe control grid ;and accelerating electrode having .a cylindrical side wall coaxial, with and, of substantially the same diameter'as said accelerating electrode and having a transverse bottom wall opposite the transverse wall of said control grid provided with an eccentric aperture aligned with said control grid aperture on a line parallel to said major axis, at least one support rod of electrically insulating material connected to said accelerating electrode, screen grid, and control grid for maintaining the same in mutually coaxial relation, a cathode within said control grid having an electron emitting surface opposite said control grid aperture, and a supporting arm connected to said cathode and anchored in an extension of said support rod, said accelerating electrode and screen grid being adapted to be maintained at different potentials such as to form an electrostatic field therebetween for deflecting toward said major axis electrons and ions of a beam passing through said control grid and screen grid apertures, whereby upon subjection to a magnetic' field in theyvicinity of said electrostatic field the electrons of the beam can be directed through i said accelerating electrode exit aperture in a path coincident with said major axis.

5. A cathode ray tube comprising an envelope having a tubular neck, an electron gun within said neck comprising a cylindrical first electrode having an axis defining the major axis of the electron gun and having at one end a transverse partition formed with a coaxial electron exit aperture of substantially the same diameter as said'first electrode, means for supporting said first electrode in coaxial relation with the neck, a second electrode having a cylindrical side wall, means for supporting said second electrode with its side wall in coaxial relation with the first electrode and spaced therefrom so as to form a gap therewith, said first and second electrodes being adapted to be maintained at 'diiferent potentials so as to form in said gap an electrostatic electron lens for deflecting toward the axis of said first electrode electrons passing through a part of the lens transversely spaced from the axis of said first electrode, means for producing a mixed beam of electrons and ions having a path parallel to said first electrode axis but transversely spaced therefrom so as to pass through said transversely spaced part of said lens, and a single magnet external to said neck providing a magnetic field transverse to the axis of said first electrode in the region of said electrostatic lens for diverting the electrons of said'mixed beam into a path. extending throughtthe exit aperture of said first electrode substantially coincident with said first electrode axls.

6. A cathode ray tube comprising an envelope having a tubular neck, an electron gun within said neck comprising a tubular accelerating electrode having an axis defining the major axis of the electron gun and having at one end a transverse wall provided with a coaxial elec:

tron exit aperture and defining at its other end a coaxial opening, means for supporting said accelerating electrode in coaxial relation with the neck, a cup-shaped second electrode having a cylindrical side wall of substantially the same diameter as said accelerating electrode and having a transverse bottom wall, means for supporting said second electrode in coaxial relation with the accelers of said electron lens, means for producing a mixed beam of electrons and ions having a path which extends through said aperture of said second electrode parallel to the accelerating electrode axis so as to pass through said transversely spaced part of said lens, said beam producing means including a control grid having an aperture concentrically aligned with said second electrode aperture on a'line parallel to said axis, and a magnet external to said neck providing a magnetic field in the region of said electrostatic lens for diverting the electrons of said mixed beam into a path extending through the exit aperture of said accelerating electrode substantially coincident with said accelerating electrode axis.

References Cited in the fileof this patent UNITED STATES PATENTS 2,472,766 Woodbridge June 7, 1949 2,565,533 Szegho Aug. 28, 1951 2,596,508 Phillips May 13, 1952 2,604,599 Breeden July 22, 1952 2,680,204 Swedlund June 1, 1954 2,732,511 Dichter Jan. 24, 1956 2,744,208 1956 Swedlund May 1, 

